1. Field of the Invention
This invention relates to a safety system for protecting the environment from radioactive contamination from a nuclear plant in case of nuclear accidents, particularly of the type where all containment safeguards have failed and containment failure is imminent. Such accidents are generally classified as being of the class 9 type which would involve fuel damage in the reactor vessel, pipe breakages and loss of heat removal, leading to a melting of reactor core and its collapsing to the bottom of the containment building. During such occurrences, hot steam and gases carrying radioactive fission products are released into the containment building and build up a pressure which may lead to containment failure, manifesting itself by a discharge of the steam and gases from the containment building, for example, through cracks and pipe fittings. Such a discharge of radioactive vapors and gases poses a threat to the environment and heretofore no provisions have been made to control the outflow of gases from the containment building of a nuclear reactor and to scrub such gases from fission products as a last safety measure when containment failure is imminent, particularly as a result of a nuclear accident of the class 9 type.
2. Description of the Prior Art
Treating gases which have escaped into the containment area as a result of an accident, by removing at least one part of the fission products therefrom prior to their release to the atmosphere is generally known. F. W. Kleimola U.S. Pat. No. 4,210,614 discloses a passive protection system in case of a loss of coolant accident in a nuclear power plant. Among other measures to prevent the melting of fuel and to enhance a rapid decrease of pressure in the containment building, the pressure of the steam released into the containment building as a result of an accident breaks rupture discs in deluge tanks. The liquid in the deluge tanks contains fission product "getters" for reducing the radioactivity of the vapors and gases in the containment building. This system presupposes a successful retention of the gases and vapors within the containment building and makes no provision for a final treatment of gases when escape thereof from the containment building is unavoidable.
Bevilacqua et al U.S. Pat. No. 3,459,635 discloses a system which, in case of an accident, guides the pressurized vapor from the containment area into containers where the vapors are condensed by a liquid stream. Further, the atmosphere of the containment is circulated through the containers and through a serially connected conventional filtering and purifying arrangement for removing radioactive material from the gases. Thereafter the gases are reintroduced into the containment area or, if sufficiently purified, released to the atmosphere. The vapor circuit through the purifying arrangement is maintained in motion by a circulating pump.
Long U.S. Pat. No. 3,105,028 provides, in case of an accident, for a coolant removal from the reactor system into a gas tank and therefrom into a carbon dioxide absorption tower in which, among others, solid fission product fragments are retained.
Kodama et al U.S. Pat. No. 4,416,850 discloses a spraying system installed in a primary containment vessel to condense the radioactive vapor which fills the vessel and to cool the gases therein. Radioactive water-soluble gases are dissolved in the sprayed water. Thereafter sprayed and condensed water are separated.
While the above-outlined prior art systems provide, to a certain extent, for the removal of fission products from the gases and vapors which build up pressure in the containment as a result of an accident, such safety systems have not been designed for a final treatment of the gases and vapors when containment failure is imminent and a direct discharge of the containment atmosphere into the surrounding environment is unavoidable.